Solvents play a major role in determining the course, the regiochemistry and stereochemistry,a nd the rates of chemical and biochemical reactions. Therefore it is of importance to study solvent effects in detail, and to develop methods for predicting their effect on a given process. A new solvent effect model has been developed that is based on ab initio molecular orbital theory, and does not employ any empirical parameters. It has been tested on a few systems, and was found to give results in agreement with experimental measurements. The plan is to carry out both experimental and computational studies of effects in systems that are of importance in natural product synthesis and in biochemical studies. Much of the initial work will be concerned with further tests of the model using a number of reactions that span a range of changes in polar character during the reaction. If these tests are successful, it will be possible to make predictions of effects that should be observed. Further development of the model is planned in order to include the effects of hydrogen bonding, changes in cavity size during the reaction, and changes in dynamical solute-solvent interactions. The results of this investigation should allow a much better understanding of how solvents interact with organic compounds.